1. Field of the Invention
The present invention relates to an apparatus and method for mounting an aircraft engine to an aircraft, and more particularly to such an apparatus and method particularly adapted to meet engine mounting requirements such as those encountered in mounting an aft body mounted counter-rotation propfan engine.
2. Background Art
The mounting structure of an aircraft engine must be able to withstand transverse loads (i.e. vertical and lateral loads resulting from gravitational forces and also "G" forces), thrust loads (exerted in a forward direction during flight and in an opposite direction during thrust reversal), gyroscopic loads (pitch and yaw) and also engine generated torque loads. These torque loads can result from the rotating components of the engine acting on the air mass, with the resistance of the air mass in turn being reacted into the engine and through the engine housing to the engine support structure, and more severe torque loads can result from vertical loads, engine seizure, or catastrophic failure of engine rotor due to fan blade-out.
One of the problems in designing a modern day aircraft is the matching of the engine to the rest of the airplane. In modern day aircraft, the overall structure of the aircraft is commonly designed by an airplane manufacturing company, and this is generally a blend of aerodynamic considerations, structural considerations, as well as many other considerations. On the other hand, the engines are commonly designed by an engine manufacturer, and while the engine manufacturer designs the engine to meet the major design requirements of the airplane manufacturer, the designer of the engine in turn imposes certain requirements upon the airplane manufacturer, such as structural requirements. More specifically, the engine designer is faced with the problems of how to react the rather substantial loads generated by the engine into the engine structure and in turn transmit these loads from the engine structure into the main structure of the aircraft. Thus, it sometimes happens that the structural pattern envisioned by the aircraft designer relative to the engine mounting would not correspond to the pattern desired by the engine manufacturer. Further, it is not always practical for the engine designer to keep modifying the engine design to fit the exact requirements of various aircraft manufacturers, since the same basic engine design might be used for a variety of designs of different airplane manufacturers. Another quite serious problem is that the engine should be mounted and arranged so as to minimize any adverse effect of unwanted transmission of noise and vibrations into the passenger area.
The problem areas outlined above become more serious with turboprop or turbofan engines. While turboprop engines offer substantial advantages in fuel savings over the turbofan engine, cabin noise propagated by the counter rotating propellers of the turboprop engine are of serious concern. Another problem is that there can be substantial energy release in case of propeller blade failure, and the shock caused by this sudden release in energy must be dampened, not only to provide passenger comfort, but also to protect the airframe structure. Further, there is the problem of generating substantial torque loads in the engine, particularly in a situation where one of the counter rotating propeller blades is not operational.
Thus, there exists a need to provide an engine mounting system which meets the following design criteria:
a) The engine mount system must have the capability of reacting vertical, side, thrust and torque loads as well as pitch and yaw moments. Further, this must be done in a manner so that the locations at which these loads are imparted into the aircraft structure are optimized. PA1 b) The engine mount system must be designed to have dual load paths to meet failsafe requirements; PA1 c) The engine mount system must be designed with fuse pins to meet nacelle separation requirements; PA1 d) It must be designed to have vibration isolators for interior cabin noise and shock damping in case of engine unbalance due to propeller blade failure; PA1 e) It must be designed to carry an unbalanced load (i.e. currently designed for one complete blade out on each rotor or two on either rotor); and PA1 f) The engine mount system must have the capability of allowing for radial and longitudinal thermal growth of the engine.
Further, the mount system should meet the requirements of ease of manufacture, installation, removal and maintenance.
The design of the present invention was made to satisfy these design criteria.
A search of the patent literature has disclosed a number of patents, and these are discussed below.
U.S. Pat. No. 4,318,516--Cole relates to a mounting system for an aircraft engine. This is a wing mounted engine where there is a mounting strut which extends downwardly and laterally outwardly from the wing. Thus, the weight of the engine tends to apply to the spars of the wing a moment which is opposite to the moment that is applied by the normal lift forces exerted on the wing. The purpose of this design is to relieve to some extent the total bending moment on the spars. FIG. 3 shows a first embodiment, where there is a tube 9 which is mounted to the front and rear wing spars 7 and 8 by means of two mounts 11 and 12. The forward mount 11 permits forward to rear slide motion of the mounting tube 9, while the rear tube 12 apparently has a fixed connection to the tube 9. Specifically, there is an arm 13 connected to the tube 9 and also to a pin 14 and the spar 8, and this resists rotation of the tube 9 about its lengthwise axis. The tube 9 is in turn connected to the nacelle, but the details of this connection are not shown. A second embodiment is shown in FIG. 4, and there are three wing spars 20, 21 and 22. There is a rear mounting tube 25 connected to the middle and rear spar 21 and 22. This tube 25 is connected to a flanged member 26 to resist torsional loads. The forward bearing 24 permits a certain amount of axial movement between the tube 23 and the mount 24. The overall purpose of the device shown in this patent is to place the mass of the engine at a location so that the weight of the engine will provide desirable bending moments in the wing structure. However, this patent does not contain any significant teaching of how to match the structural load transmitting characteristics of the engine to those of the aircraft structure.
U.S. Pat. No. 2,718,756--McDowall shows a mounting and support structure for an aircraft gas turbine power plant having reduction gearing. There are two rear motors B having output shafts extending forwardly therefrom and mounted in struts 26. The struts 26 are mounted to a housing of a gear reduction drive A. There are upper struts 37 positioned above the struts 26, and these extend from the upper part of the forward engine compressors 12 to an upper location of the gear reduction housing.
U.S. Pat. No. 2,738,647--Hill shows a gas turbine frame structure, where the power output and gas producing sections of the engine are interconnected by a frame structure comprising three triangularly arranged longitudinal frame members 76 disposed symmetrically about the longitudinal axis of the engine.
U.S. Pat. No. 3,222,017--Bobo shows a mounting for a jet engine having a rearwardly positioned fan casing. The thrust mounting 6 is in the form of a ring that surrounds the casing 4. There is a thrust ring 7 extending around and rigidly fixed to the fan case 4. There are also two hollow ring-like members 17 that are rigidly secured to a supporting plate 18 fixed to the aircraft structure. The members 17 are filled with a force transmitting medium 20 which is preferably a body of resilient material such as rubber. The ring structure 7 transmits its loads into the rubber-like medium 20 which in turn transmits it through the ring member 17 to the structure 18. Thus, this patent discloses a load carrying member mounted to the engine which transmits its loads through a yielding material, such as rubber.
U.S. Pat. No. 3,448,945--Ascani, Jr. discloses what is called a "convertible propulsion package", where a conventional engine can be replaced with a VTOL engine and nacelle.
U.S. Pat. No. 3,750,983--Morris shows an engine mounting structure by which a jet engine is mounted to a rigid beam 24. There is a rear mounting linkage (see FIG. 4) which apparently resists both vertical loads and torque loads exerted about the longitudinal axis of the engine. There is a downwardly and forwardly extending linkage structure 34 which resists the tension loads exerted by the engine. Finally, there is a forward support linkage which supports the shroud positioned around the fan.
U.S. Pat. No. 3,848,832--Stanley et al shows an aircraft engine mounting installation where there is a pair of rigid support beams extending forwardly from the front spar. There is an inverted U-shaped transom interconnecting the forward end portions of the beam, and the engine for the aircraft is suspended from the transom structure.
U.S. Pat. No. 3,907,220--Amelio discloses a mounting structure for a jet engine where there are lateral inboard and outboard rear engine mounts. There is a third redundant rear mount provided beneath the engine which does not contribute any significant support for the engine, but which, in the event of failure of either of the two lateral rear mounts, cooperates with the other rear mount to provide a provisional rear support of the engine.
U.S. Pat. No. 4,013,246--Nightingale illustrates an engine mounting system where there is a forward mount connected to the fan case, and a rear mount connected to the core engine. A pair of struts 58 and 60 are provided to resist the tension loads exerted by the force of the engine.
U.S. Pat. No. 4,044,973--Moorehead shows a mounting structure for an engine that is mounted from a laterally extending support beam. There is a forward mounting member fixedly connected to a forward laterally extending support beam, and this structure extends upwardly and then downwardly in the form of a yoke to connect to the fan case by means of shock absorbing mounts. There is a rear support structure extending from a rear laterally extending beam, and this is connected by a shock mount to the fore engine.
U.S. Pat. No. 4,055,041--Adamson shows a gas turbine engine where the outer nacelle is entirely supported from the engine by means of a webbed structure comprising radially extending struts.
U.S. Pat. No. 4,316,296--Hall et al is directed primarily to a device for connecting the surrounding inlet structure of the engine to the casing. Two toroidally shaped members are positioned between respective annular flanges to allow relative angulation, while allowing loads to be transferred between the two members. Also, a mounting system for the engine is shown where there are fore and aft mounting members, along with downwardly and forwardly extending mounting struts to receive tension loads resulting from thrust of the engine.
U.S. Pat. No. 4,458,863--Smith shows a turbofan engine having a support system somewhat similar to the Hall et al patent mentioned immediately above. The inlet is coupled to the engine fan case by means of a plurality of fluid filled pistons and cylinder assemblies that transmit only axially oriented loads from the inlet to the fan case.
U.S. Pat. No. 4,474,346--Murphy et al shows a cowl structure for a gas turbine engine where there is a protective belt surrounding the fan section.
U.S. Pat. No. 4,555,078--Grognard shows an engine mounting system where there is a flexmount member 2 connecting to the engine by front and rear attachment devices 11 and 12. An upper pylon 8 is connected to the flexmount structure 2, and the engine mounts are housed in the upper pylon 8. The apparatus is arranged so that the engine can operate in a "cowl load sharing mode" where the suspension apparatus is in a locked position. Further, the engine with its cowling can be rigidly secured for repair and servicing when the suspension apparatus is used in its non-free position.